In this lab, we will use lists to implement a lot of string processing. The type String is not decomposable as a list, but strings can be converted to lists of Char as follows:
"Some string".toList
For this reason, we will use the following aliases:
type Str = List[Char] type Email = Str
Throughout this lab, use higher-order functions (map, foldRight, foldLeft, filter, zip, partition, etc) whenever possible.
In what follows, we shall encode a gradebook as a list of pairs (<name>,<grade>), where <name> is a String and <grade> is an Int. Example:
type Gradebook = List[(String,Int)] //the type Gradebook now refers to a list of pairs of String and Int val gradebook = List(("G",3), ("F", 10), ("M",6), ("P",4))
Add this type alias to your code before solving the following exercises.
6.1.1. Write a function which adds one point to all students which have a passing grade (>= 5), and leaves all other grades unchanged.
def increment(g: Gradebook): Gradebook = g.map(???)
6.1.2. Find the average grade from a gradebook. You must use foldRight.
def average(g: Gradebook): Double = ???
6.1.3. Write a function which takes a gradebook and returns the percentage of failed vs. passed students, as a pair (x,y).
def percentage(g: Gradebook): (Double,Double) = ???
6.1.4. Write a function which takes a gradebook and returns the list of names which have passed. Use filter and map from Scala.
def pass(g: Gradebook): List[String] = ???
6.1.5 Write a function which takes a gradebook and reports all passing students in descending order of their grade.
def honorsList(g: Gradebook): List[String] = ???
6.1.6. We extend the type Gradebook to:
type Name = String type Lecture = String type ExtGradebook = List[(Name,Lecture,Int)] val egradebook = List(("John","FP",4)) // the first string is the student name, the second is the course, and the final integer is the grade
Write a function which reports all students that have failed at least one grade (each student will be reported once):
def atLeastOneFail(g: ExtGradebook): List[Name] = ???
6.1.7.(!) Write a function groupBy, which is a generalisation of the previous exercise:
def groupBy[A,B](l: List[A])(criterion: A => B): List[(B,List[A])] = ???
The function groupBy takes a list with elements of type A, a criterion A ⇒ B and produces a list of pairs (c, lp) : (B,List[A]) with the property that each member of the list lp satisfy the criterion with the value c. Suppose f: A ⇒ B is a criterion. Two elements a : A and b : A satisfy the criterion f iff f(a) == f(b). Examples:
groupBy(List("john", "mary", "mihai"))(_.size) = List((4,List("john","mary")), (5, List("mihai")))
groupBy(List((1,2), (2,1), (3,3))(p => p._1 + p._2) = List((3,List((1,2),(2,1))), (6, List((3,3)))
6.2.1. Write a function which takes a list of emails and extracts the prefix (e.g. example@domain.com becomes example).
def getNames (l: List[Email]): List[Email] = ???
6.2.2. Write a function which filters out emails belonging to a specific Top-Level-Domain (e.g. those than end in com).
def removeTLD(l: List[Email], tld: Str): List[Email] = ???
6.2.3. Write a function which checks is there exist identical names under different domains in a list of emails (e.g. ana@amazon.com and ana@gmail.com)
def containsDuplicates(l: List[Email]): Boolean = ???
6.2.4. Write a function which reports the number of duplicates of names under different domains in a list of emails. (e.g. [“ana@aol.com”, “ana@aol.ro”, “ana@amazon.com”, “jim@cx.com”, “mary@mail.com” , “mary@mail.ro”] will produce: 2 since there are two duplication instances: for ana and for mary.
def countDuplicates(l: List[Email]): Int = ???
6.2.5. Write a function which reports all duplicates of names under different domains in a list of emails. (e.g. [“ana@aol.com”, “ana@aol.ro”, “jim@cx.com”, “mary@mail.com” , “mary@mail.ro”] will produce: [ [“ana@aol.com”, “ana@aol.ro”], [“mary@mail.com” , “mary@mail.ro”]]
def extractDuplicates(l: List[Email]): List[List[Email]] = ???
6.2.6. Write a function which removes all duplicates of names under different domains in a list of emails. (e.g. [“ana@aol.com”, “ana@aol.ro”, “jim@cx.com”, “mary@mail.com” , “mary@mail.ro”] will produce: [ [“ana@aol.com”, “ana@aol.ro”], [“mary@mail.com” , “mary@mail.ro”]]
def extractDuplicates(l: List[Email]): List[List[Email]] = ???